The present invention relates to the field of overcoat materials, and more specifically relates to overcoat materials functioning as relaxation coatings applied of electrode grids.
There are known or proposed systems for electrostatically agitating or moving fine particulate materials, such as marking material (e.g., toner) and the like. One such system is described in U.S. patent application Ser. No. 09/163,839, in which a grid of small and closely spaced electrodes are connected to a driver circuit such that a phased d.c. travelling electrostatic wave is established along the grid. Charged particulate material is transported by the electrostatic wave in a desired direction, at a desired velocity. Other such systems cause marking material particles to be agitated from a surface so as to be proximate a receiving surface such as a photoreceptor.
It is known to encapsulate electronic devices, such as integrated circuits, in protective coatings. Such coatings may provide physical protection from scratches, and a moisture barrier between the devices and the ambient environment. However, such materials are generally not used as top-surface dielectrics. Furthermore, such insulation and passivation layers typically have very high resistivities to avoid possible electrical shorts between covered leads.
We have discovered that there are a variety of criteria which overcoats for virtually all electrode grids of the type described above should address. First, it is desirable to provide a planarized surface over which the particulate material may reside or travel. Such a surface eliminates the problem of particulate material becoming trapped between the electrodes. Second, it is desirable to provide a material over the electrodes to provide rapid charge dissipation at a selected time constant. Third, arcing between electrodes must be prevented. Fourth, it is desirable that the overcoat provide a degree of wear resistance, especially in the case of marking material transport. Finally, it is important that such a layer be chemically stable. That is, the layer material must not react with the particulate material nor change characteristics in the presence of the operating environment. However, no known material to date has been able optimize each of these desired attributes.